U.S. patent number 5,637,259 [Application Number 08/567,102] was granted by the patent office on 1997-06-10 for process for producing syngas and hydrogen from natural gas using a membrane reactor.
This patent grant is currently assigned to Natural Resources Canada. Invention is credited to Shamsuddin Ahmed, Safaa Fouda, Jan Z. Galuszka, Raj N. Pandey.
United States Patent |
5,637,259 |
Galuszka , et al. |
June 10, 1997 |
Process for producing syngas and hydrogen from natural gas using a
membrane reactor
Abstract
Novel procedures are described for the production of syngas fuel
intermediates from abundantly available natural gas. The novel
procedures include: (a) providing a double tubular hydrogen
transfer reactor having an inner tubular wall defining a heated
reaction zone containing a catalyst and an outer tubular wall
defining an annular zone between the tubular walls, said inner
tubular wall including a hydrogen semipermeable membrane portion
adapted to permit diffusion of hydrogen therethrough from the
reaction zone to the annular zone while being impervious to other
gases, (b) passing through said catalytic reaction zone of a
feedstock comprising a mixture of methane and oxygen or a mixture
of methane and carbon dioxide or a mixture of methane, carbon
dioxide and oxygen, (c) continuously removing from the reaction
zone at least part of the hydrogen being formed by diffusion
thereof through said hydrogen semipermeable membrane into said
annular zone, (d) continuously removing diffused hydrogen from said
annular zone and (e) continuously removing a product mixture of
carbon monoxide and hydrogen from the reaction zone.
Inventors: |
Galuszka; Jan Z. (Nepean,
CA), Fouda; Safaa (Ottawa, CA), Pandey; Raj
N. (Guelph, CA), Ahmed; Shamsuddin (Guelph,
CA) |
Assignee: |
Natural Resources Canada
(Ottawa, CA)
|
Family
ID: |
24265727 |
Appl.
No.: |
08/567,102 |
Filed: |
December 4, 1995 |
Current U.S.
Class: |
252/373; 423/652;
423/650; 423/359; 95/41 |
Current CPC
Class: |
C01B
3/38 (20130101); C01B 3/386 (20130101); B01J
19/2475 (20130101); C01B 3/501 (20130101); C01B
3/505 (20130101); B01J 8/06 (20130101); B01J
8/009 (20130101); C01B 2203/1241 (20130101); C01B
2203/1064 (20130101); C01B 2203/0261 (20130101); C01B
2203/1011 (20130101); C01B 2203/047 (20130101); C01B
2203/0238 (20130101); Y02P 20/141 (20151101); C01B
2203/1082 (20130101); C01B 2203/041 (20130101); Y02P
20/142 (20151101); B01J 2208/00212 (20130101) |
Current International
Class: |
C01B
3/38 (20060101); C01B 3/00 (20060101); C01B
3/50 (20060101); B01J 19/24 (20060101); B01J
8/00 (20060101); B01J 8/02 (20060101); B01J
8/06 (20060101); C07C 001/02 () |
Field of
Search: |
;252/373
;423/650,652,359 ;95/41 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ivy; C. Warren
Assistant Examiner: Padmanabhan; Sreeni
Claims
We claim:
1. A process for producing a fuel intermediate comprising a mixture
of carbon monoxide and hydrogen from natural gas that includes:
(a) providing a double tubular hydrogen transfer reactor having an
inner tubular wall defining a heated reaction zone containing a
catalyst and an outer tubular wall defining an annular zone between
the tubular walls, said inner tubular wall including a hydrogen
semipermeable membrane portion adapted to permit diffusion of
hydrogen therethrough from the reaction zone to the annular zone
while being impervious to other gases, said membrane portion
comprising an inert, porous tubular substrate at least 1 mm thick
and having deposited on a surface thereof a dense membrane film
composed of a metal or a material selected from the group
consisting of silica, alumina, zirconia or zeolite, said dense film
having a thickness in the range of from 1 .mu.m to about 25
.mu.m,
(b) passing through said catalytic reaction zone of a feedstock
comprising a mixture of methane and oxygen or a mixture of methane
and carbon dioxide or a mixture of methane, carbon dioxide and
oxygen,
(c) continuously removing from the reaction zone at least part of
the hydrogen being formed by diffusion thereof through said
hydrogen semipermeable membrane into said annular zone,
(d) continuously removing diffused hydrogen from said annular zone
and
(e) continuously removing a product mixture of carbon monoxide and
hydrogen from the reaction zone.
2. A process according to claim 1 wherein a feedstock comprising a
mixture of methane and oxygen is subjected to partial
oxidation.
3. A process according to claim 2 wherein the partial oxidation is
carried out at atmospheric pressure and a temperature in the range
of 500.degree.-750.degree. C.
4. A process according to claim 2 wherein the feedstock is natural
gas.
5. A process according to claim 4 wherein the catalyst is a
supported palladium catalyst.
6. A process according to claim 4 wherein said membrane comprises a
porous alumina tube having a palladium film superimposed on the
inner wall thereof.
7. A process according to claim 1 wherein a feedstock comprising a
mixture of methane and carbon dioxide is reacted in the catalytic
reaction zone.
8. A process according to claim 7 wherein the feedstock is natural
gas.
9. A process according to claim 8 wherein catalytic reaction is
carried out at atmospheric pressure and a temperature in the range
of 500.degree.-750.degree. C.
10. A process according to claim 8 wherein the catalyst is a
supported palladium catalyst.
11. A process according to claim 8 wherein said membrane comprises
a porous alumina tube having a palladium film superimposed on the
inner wall thereof.
Description
BACKGROUND OF THE INVENTION
This invention relates to a process for the production of a fuel
intermediate consisting of a mixture of hydrogen and carbon
monoxide from natural gas.
Natural gas, in which methane is the principal constituent, is an
abundant resource with a world reserve estimated at over
100.times.10.sup.12 m.sup.3. Carbon dioxide is a major byproduct in
many industries. At present, there is no known technology for
utilization of carbon dioxide. However, considerable effort is
being expended to develop processes for conversion of methane to
value-added products. Major areas of focus include partial
oxidation to methanol, oxyhydrochlorination to methyl chloride and
oxidative coupling to ethylene.
There is also considerable interest in the conversion of natural
gas to a mixture of carbon monoxide and hydrogen, frequently
referred to as synthesis gas (syngas). Renewed interest in
synthesis gas production has been stimulated by a variety of
environmental and technological issues. It is estimated that the
global methanol market will need an additional 10 million metric
tons per annum of methanol capacity by the year 2000. Methanol can
be used either as a transportation fuel in a modified vehicular
engine, or can be converted to gasoline (by Mobil's MTG Process) or
reacted with isobutylene to produce MTBE which is an important
ingredient for reformulated gasoline. In the United States alone,
hydrogen production capacity now under construction totals more
than 220 million SCFD in conjunction with new distillate
hydrotreaters. Also, ammonia production is still the largest single
consumer of syngas. The importance of syngas is well recognized in
the chemical industries, in the production of synthetic fuels by
Fischer-Tropsch process and mixed alcohols. Because a mixture of
carbon monoxide and hydrogen can be readily transformed into
gasoline range hydrocarbons, it will be referred to hereinafter as
"fuel intermediate". Existing technology for the production of
synthetic gas involves catalytic steam reforming of feedstocks such
as natural gas, light and heavy oils and coal. One such process is
described in Miner et al., U.S. Pat. No. 5,229,102, issued Jul. 20,
1993. However, a number of disadvantages arise in the existing
technology. Steam reforming is strongly endothermic (energy
intensive), requires high temperatures (>850.degree. C.) and
high pressures (>20 atm) to achieve acceptable yields, causes
severe coking of the catalysts, and produces a product mixture with
H.sub.2 /CO ratio >3 (with natural gas as feedstock) and with
H.sub.2 /CO ratio <0.7 (with coal and refinery oil as feedstock)
both of which are unsuitable for most applications without
secondary reforming. On the whole, the existing technology is
highly capital intensive, accounting for more than 70% of the total
investment and operating costs in methanol production based on
natural gas conversion process. Syngas is also produced by
non-catalytic partial oxidation (POX) of methane, e.g. as described
in Fong et al, U.S. Pat. No. 5,152,975, issued Oct. 6, 1992.
However, operation at high temperatures (>1300.degree. C.) and
high pressures (>150 atm) is essential to obtain high
selectivities by this process. The overall comparative economics of
syngas production technologies continues to favour steam methane
reforming despite the drawbacks mentioned above. The growing
interest in C-1 chemistry to accomplish large-scale conversion of
natural gas to liquid fuel has created a need to find a
cost-effective technology for the production of syngas fuel
intermediate.
Therefore, one objective of the present invention is to provide
novel routes for the production of syngas fuel intermediate from
abundantly available natural gas. These routes involve less capital
investments and operating costs than existing steam reforming
technology and avoid the necessity for severe operating conditions
of high temperature and high pressure of convention technology.
Another objective of this invention is to exploit the potential of
a membrane reactor technology to attain much higher conversions of
natural gas and selectivities to fuel intermediate than those
achievable in a conventional reactor.
Another objective of this invention is to provide a highly
economical route for in situ production of pure hydrogen from
natural gas by means of partial oxidation and reaction with carbon
dioxide in a hydrogen semipermeable chemical reactor. In contrast
to existing steam reforming technology, this route does not require
expensive down stream separation.
SUMMARY OF THE INVENTION
This invention relates to a process for producing a fuel
intermediate comprising a mixture of carbon monoxide and hydrogen
from natural gas. The process steps include: (a) providing a double
tubular hydrogen transfer reactor having an inner tubular wall
defining a heated reaction zone containing a catalyst and an outer
tubular wall defining an annular zone between the tubular walls,
said inner tubular wall including a hydrogen semipermeable membrane
portion adapted to permit diffusion of hydrogen therethrough from
the reaction zone to the annular zone while being impervious to
other gases, (b) passing through said catalytic reaction zone of a
feedstock comprising a mixture of methane and oxygen or a mixture
of methane and carbon dioxide, or a mixture of methane, carbon
dioxide and oxygen, (c) continuously removing from the reaction
zone at least part of the hydrogen being formed by diffusion
thereof through said hydrogen semipermeable membrane into said
annular zone, (d) continuously removing diffused hydrogen from said
annular zone and (e) continuously removing a product mixture of
carbon monoxide and hydrogen from the reaction zone.
A first embodiment of the invention (hereinafter referred to as
Process 1) relates to a novel and efficient process for the
production of a fuel intermediate consisting of a mixture of carbon
monoxide and hydrogen from natural gas by partial oxidation,
typically at temperatures in the range of about 500.degree. to
750.degree. C. The reaction is conveniently carried out at
atmospheric pressure, although elevated pressure may also be used.
The reaction is conducted in a hydrogen transfer reactor in which
the product hydrogen is selectively and continuously withdrawn from
the reaction zone by diffusion through the semipermeable membrane
wall of the reactor.
The main chemical reactions which occur during partial oxidation of
natural gas to carbon monoxide and hydrogen are:
______________________________________ H.sup.o .sub.298K (kJ/mol)
______________________________________ CH.sub.4 + 2 O.sub.2
.fwdarw. CO.sub.2 + 2 H.sub.2 O -802 (1) CH.sub.4 + H.sub.2 O
.revreaction. CO + 3 H.sub.2 206 (2) CH.sub.4 + CO.sub.2
.revreaction. 2 CO + 2 H.sub.2 247 (3) CO + H.sub.2 O .fwdarw.
CO.sub.2 + H.sub.2 -41 (4)
______________________________________
Initially, methane undergoes combustion [reaction (1)] producing
carbon dioxide and water. During this step, oxygen may be entirely
consumed. The formation of carbon monoxide and hydrogen is the
result of secondary reactions of unreacted methane with water and
carbon dioxide [reactions (2) and (3)]. The final product
composition is further affected by the water gas shift reaction
[reaction (4)].
Reactions (2) and (3) are reversible endothermic reactions. The
reversible nature of these reactions imposes a limit, determined by
the position of thermodynamic equilibria, on the achievable
conversion and yields of carbon monoxide and hydrogen at a given
temperature in a conventional reactor. Because of high
endothermicity of these reactions, this limit is well below
commercially acceptable levels, unless reaction temperature is very
high (>800.degree. C.). However, if one of the reaction products
(for example, hydrogen) is selectively and continuously removed
from the reaction zone, the equilibrium limitations of a
conventional reactor can be circumvented. The withdrawal of
hydrogen displaces the equilibria of reactions (2) and (3) to the
product side. Therefore, the overall achievable conversion is
expected to be much greater than that dictated by thermodynamic
equilibrium. Alternatively, this offers the possibility of
obtaining a given level of conversion at a much lower operating
temperature than realized in a conventional reactor.
Process I of this invention relates to achieving this objective by
conductive methane partial oxidation reaction in a reactor
comprising of a hydrogen semipermeable membrane wall. The reactor
allows hydrogen to diffuse out through its wall but is impervious
to other gases, thereby continuously driving the equilibria of
reactions (2) and (3) to the product side.
A variety of known catalysts containing various metals, such as
iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium,
platinum, cerium etc., may be used for the process of invention.
The metal is usually supported and a large variety of supports may
be used, such as alumina, silica, magnesia, zirconia, yttria,
calcium oxide, zinc oxide, perovskites, lanthanide oxides, etc.,
e.g. as described in Tsang et al., Catalysis Today, 23, 3, (1995),
incorporated herein by reference. These supported catalysts may be
used in either fixed bed or fluidized bed form.
The membrane is preferably in the form of a thin film of a metal,
such as palladium or its alloys, or thin film of silica, alumina,
zirconia or a zeolite. The film thickness typically ranges from 1
.mu.m to about 25 .mu.m. A preferred thin film is palladium with a
thickness of about 5 to 15 .mu.m. To assure the mechanical
strength, the thin film is preferably supported on an inert, porous
tubular substrate at least 1 millimeter thick, e.g. a porous
ceramic material such as a porous alumina or porous Vycor.TM. glass
typically having pore sizes larger than about 40 nm, preferably
about 4-300 nm. The thin film is deposited on the porous substrate
by various techniques, e.g. electroless-plating, electroplating,
sputtering, chemical vapour deposition, sol-gel deposition etc. The
supported membrane must be capable of selectively passing hydrogen
to the exclusion of the other gases, preferably with a good flux.
It is also preferable to maintain a hydrogen .DELTA.P across the
membrane.
According to one preferred aspect of Process I of this invention,
supported palladium catalysts (wherein the support is
.alpha.-Al.sub.2 O.sub.3, .gamma.-Al.sub.2 O.sub.3, SiO.sub.2 and
ZrO.sub.2) are used for the partial oxidation of methane to syngas
fuel intermediate in a conventional reactor. The catalysts produce
the fuel intermediate at reaction temperatures 500.degree. C. and
above, and CH.sub.4 /O.sub.2 feed ratios from 6 to 1. The
conversion of methane and selectivity to a fuel intermediate
increase with reaction temperature, the latter reaching more than
95% between temperatures 600.degree.-650.degree. C. Examination of
conventional reactor effluent composition in the light of
thermodynamic equilibrium constants showed that reactants and
products attained equilibrium composition according to reactions
(2), (3) and (4) under most of the experimental conditions. This
indicated that scope existed to take advantage of membrane reactor
technology to enhance the partial oxidation of natural gas to a
syngas fuel intermediate.
According to another preferred aspect of Process I of this
invention, a hydrogen transfer reactor was prepared. It consisted
of a palladium membrane superimposed on the inner wall of an
asymmetric porous alumina tube (Membralox.TM.) supplied by ALCOA.
The palladium film was deposited by an electroless plating
technique. The plating mixture consisted of palladium-amine
complex, hydrazine, EDTA and ammonium hydroxide. Hydrazine acted as
the reducing agent, while EDTA acted as an effective stabilizer
against homogeneous decomposition of the mixture. Plating was done
at .apprxeq.55.degree. C. and pH=12. The deposition was continued
for approximately 30 h, with renewal of the plating solution every
half hour. Before plating, the inner surface of the porous alumina
tube was activated by subjecting to sensitization and activation
treatment using SnCl.sub.2 and PdCl.sub.2 solutions. The thickness
of the deposited film was approximately 10 .mu.m. The hydrogen
transfer reactor was assembled by placing the membrane tube inside
a stainless steel cylinder as shown in FIG. 1 and the two were
sealed gas tight at the two ends. The selective hydrogen
permeability characteristics of membrane reactor was verified.
A second main embodiment of this invention (hereinafter referred to
as Process II) offers a second process for efficient production of
syngas fuel intermediate and hydrogen from natural gas. In this
process, methane is reacted with carbon dioxide in a hydrogen
transfer reactor (packed with catalyst bed) wherein the product is
selectively and continuously removed from the reaction zone through
the semipermeable wall of the reactor.
Conversion of methane to syngas occurs according to the following
overall reaction:
The product distribution or H.sub.2 /CO ratio in the product stream
is further influenced by the water gas shift reaction:
Due to the reversible nature of reaction (3), there is a limit,
determined by the position of thermodynamic equilibrium, to the
conversion achievable of CH.sub.4 and yields of CO and H.sub.2 at a
given temperature.
Process II of this invention relates to circumventing this
equilibrium-controlled limit of conversion by taking advantage of a
hydrogen transfer reactor. Continuous and selective removal of
hydrogen from the reaction zone via diffusion through the
permselective reactor wall pushed the equilibrium towards high
conversion than achievable in a conventional closed reactor.
According to one aspect of Process II of this invention, supported
palladium is used as catalyst for production of a syngas fuel
intermediate and hydrogen by reaction of CH.sub.4 with CO.sub.2 in
a conventional closed reactor. Examination of the conventional
reactor exist stream data showed that equilibrium was reached in
reactions (2), (3) and (4) under most of the experimental
conditions. Attainment of equilibrium in the reaction (3) is of
particular importance. This implies that scope exists to exploit
membrane reactor technology to promote production of syngas and
hydrogen by reaction of CH.sub.4 with CO.sub.2.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a partial sectional elevation of a hydrogen transfer
reactor of the invention.
The reactor of this invention includes an outer tubular member 10
having a top cap 11 with an inlet nipple 12 for connection to a
CH.sub.4 /O.sub.2 supply. The bottom end of tubular member 10 is
closed by a bottom cap 13 with an outlet nipple 14 for connection
to a syngas product discharge line.
Mounted within tubular member 10 is an inner tubular member 15, a
portion of the wall of which comprises a membrane 16. Within the
membrane portion is a fixed catalyst bed 17.
Between the outer tubular member 10 and the inner tubular member 15
is an annular chamber 20 within which hydrogen passing through
membrane 16 is collected. A purge gas is passed through chamber 20
via inlet nipple 18 and outlet nipple 19. The ends of chamber are
sealed against any gas flow by means of sealing members 21.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Certain preferred embodiments of the present invention are
illustrated by the following non-limiting examples.
EXAMPLE 1
The partial oxidation of methane to a syngas fuel intermediate was
carried out in a fixed bed continuous flow double tubular hydrogen
transfer reactor as shown in FIG. 1. The inner tube (membrane tube)
of the reactor was charged with 1.0 gram of 5.0 wt %
Pd/.gamma.-Al.sub.2 O.sub.3 catalyst, prepared by incipient wetness
impregnation of the support with a solution of PdCl.sub.2 salt,
followed by drying at 120.degree. C. Before the reaction, the
catalyst was calcined at 500.degree. C. under N.sub.2 flow for 2
hours, followed by reduction at 500.degree. C. under hydrogen flow
for 2 hours. The feed stream consisting of mixture of CH.sub.4,
O.sub.2 and N.sub.2 was passed through inner membrane tube and
sweep gas (Ar) was passed through the outer shell tube. The
catalyst bed was maintained at 500.degree. C. The inner and outer
streams were analyzed separately for products and reactants by
TCD-gas chromatography. CH.sub.4, O.sub.2, N.sub.2, and CO were
analyzed with a molecular sieve 5A column employing helium as
carrier gas. CO.sub.2 was analyzed with a Porapak T.TM. column
employing helium as carrier gas. H.sub.2 was analyzed with a
molecular sieve 5A column employing argon as carrier gas. Methane
conversion and selectivity to the products were determined.
Selectivity to CO is defined on the basis of total CO and CO.sub.2
in the products. Selectivity to H.sub.2 is defined on the basis of
total H.sub.2 and H.sub.2 O in the products. The results are
reported in Table A. Included in Table A are the results of a
duplicate experiment in a fixed bed conventional flow reactor to
compare and evaluate the performance of the membrane reactor.
TABLE A ______________________________________ Enhancement in
Catalytic Conversion of Natural Gas to Syngas Fuel Intermediate and
Hydrogen by Partial Oxidation in a Hydrogen Transfer Reactor
(Catalyst: 5.0 wt % Pd/.gamma.-Al.sub.2 O.sub.3 catalyst mass: 1.0
g; Reaction Temperature: 500.degree. C.; Feed flowrate = 87 mL
min.sup.-1 ; Sweep gas flowrate = 40 mL min.sup.-1 in the case of
hydrogen transfer reactor); Feed composition (in mole %): CH.sub.4
= 37, O.sub.2 = 12.5, N.sub.2 = balance) Conventional Membrane
Reactor Reactor ______________________________________ CH.sub.4
conv. (%) 26.7 40.3 O.sub.2 conv. (%) .apprxeq.100 .apprxeq.100 CO
sel. (mol %) 20.0 63.0 H.sub.2 sel. (mol %) 68.5 85.5 CO yield (mol
%) 5.3 25.4 H.sub.2 yield (mol %) 18.3 35.5 H.sub.2 /CO mole ratio
7.0 2.8 ______________________________________
EXAMPLE 2
The partial oxidation of methane to a syngas fuel intermediate was
conducted in a fixed bed double tubular hydrogen transfer reactor
as shown in FIG. 1 using the same catalyst as that in Example 1.
The reaction temperature was 550.degree. C. All other conditions
were the same as those in Example 1. A duplicate experiment was
conducted in a fixed bed conventional reactor to compare and
evaluate the performance of the membrane reactor. The results are
reported in Table B.
TABLE B ______________________________________ Enhancement in
Catalytic Conversion of Natural Gas to Syngas Fuel Intermediate and
Hydrogen by Partial Oxidation in a Hydrogen Transfer Reactor
(Reaction Temperature: 550.degree. C.; All other conditions
including catalyst employed were the same as those in Table A)
Conventional Membrane Reactor Reactor
______________________________________ CH.sub.4 conv. (%) 34.7 45.7
O.sub.2 conv. (%) .apprxeq.100 .apprxeq.100 CO sel. (mol %) 50.9
76.3 H.sub.2 sel. (mol %) 83.5 87.0 CO yield (mol %) 17.7 34.9
H.sub.2 yield (mol %) 29.0 40.5 H.sub.2 /CO mole ratio 3.3 2.3
______________________________________
EXAMPLE 3
Partial oxidation of methane to syngas fuel intermediate was
conducted in a fixed bed double tubular hydrogen transfer reactor
as shown in FIG. 1 using the same catalyst as that in Example 1.
The reaction temperature was 350.degree. C. All other operating
conditions were the same as those in Example 1. A duplicate
experiment was conducted in a fixed bed conventional reactor to
compare and evaluate the performance of the membrane reactor. The
results are reported in Table C.
TABLE C ______________________________________ Enhancement in
Catalytic Conversion of Natural Gas to Syngas Fuel Intermediate and
Hydrogen by Partial Oxidation in a Hydrogen Transfer Reactor
(Reaction Temperature: 350.degree. C.; All other conditions
including catalyst employed were the same as those in Table A)
Conventional Membrane Reactor Reactor
______________________________________ CH.sub.4 conv. (%) 18.4 22.9
O.sub.2 conv. (%) .apprxeq.100 .apprxeq.100 CO sel. (mol %) t 10.5
H.sub.2 sel. (mol %) 24.0 55.0 CO yield (mol %) t 2.3 H.sub.2 yield
(mol %) 4.4 13.8 H.sub.2 /CO mole ratio -- 11.9
______________________________________
Tables A to C demonstrate that conversion of CH.sub.4, and
selectivity and yield of fuel intermediate (CO and H.sub.2) are
considerably enhanced in the case of the membrane reactor. The
effect was most remarkable at 500.degree. C. and 550.degree. C. For
example, at 500.degree. C., conversion of CH.sub.4 increased from
25% in the conventional reactor to 40% in the membrane reactor.
Concomitantly, selectivity to CO increased from 20 to 63%, and to
H.sub.2 from 68 to 85%. The yield of CO increased from 5 to 25% and
that of H.sub.2 from 18 to 36%.
EXAMPLE 4
The catalytic reaction of methane with carbon dioxide producing a
syngas fuel intermediate was conducted in a fixed bed continuous
flow double tubular hydrogen transfer reactor as shown in FIG. 1.
The inner tube (membrane tube) of the reactor was charged with 1.0
g 5.0 wt % Pd/.gamma.-Al.sub.2 O.sub.3 prepared an by incipient
wetness impregnation technique. Before the reaction, the catalyst
was calcined at 500.degree. C. under N.sub.2 flow for 2 hours,
followed by reduction at 500.degree. C. under hydrogen flow for 2
hours. The feed stream consisting of a mixture of CH.sub.4,
CO.sub.2 and N.sub.2 was passed through the inner membrane tube and
sweep gas (Ar) was passed through the outer tube. The catalyst bed
was maintained at 500.degree. C. The inner and outer streams were
analyzed for products and reactants by TCD-gas chromatography.
CH.sub.4, N.sub.2 and CO were analyzed on a molecular sieve 5A
column employing helium as carrier gas. CO.sub.2 was analyzed on a
Porapak T.TM. column employing helium as carrier gas. H.sub.2 was
analyzed with a molecular sieve 5A column employing argon as
carrier gas.
Conversion of methane and carbon dioxide, yields of carbon monoxide
and hydrogen, and selectivity to H.sub.2 were determined.
Conversions were calculated in the usual way from the input and
output molar flows of the reactant. Yield of CO is defined as the
ratio of molar flow of CO in the product to the sum of molar flows
of CH.sub.4 and CO.sub.2 in the feed expressed as percentage. Yield
of H.sub.2 is defined as the ratio of molar flow of H.sub.2 in the
product to the two times of molar flow of CH.sub.4 in the feed. The
selectivity of H.sub.2 is defined on the basis of total H.sub.2 and
H.sub.2 O in the products. Because CO.sub.2 was also a reactant,
selectivity to CO has no significance. Table D includes the results
of a duplicate experiment in a closed conventional flow reactor to
compare and evaluate the performance of the membrane reactor.
TABLE D ______________________________________ Promotion of the
Catalytic Conversion of Natural Gas to Syngas Fuel Intermediate and
Hydrogen by Reaction with Carbon Dioxide in a Hydrogen Transfer
Reactor (Catalyst: 5.0 wt % Pd/.gamma.-Al.sub.2 O.sub.3 ; catalyst
mass: 1.0 g; Reaction Temperature: 550.degree. C.; Feed flowrate =
95 mL min.sup.-1 ; Sweep gas flowrate = 40 mL min.sup.-1 in the
case of hydrogen transfer reactor); Feed composition (in mole %):
CH.sub.4 = 31.5, CO.sub.2 = 26, N.sub.2 = balance) Conventional
Membrane Reactor Reactor ______________________________________
CH.sub.4 conv. (%) 17.2 37.5 CO.sub.2 conv. (%) 24.6 51.0 H.sub.2
sel. (mol %) 87.5 87.5 CO yield (mol %) 21.5 42.0 H.sub.2 yield
(mol %) 15.8 33.0 H.sub.2 /CO mole ratio 0.81 0.85
______________________________________
EXAMPLE 5
The catalytic conversion of methane to a syngas fuel intermediate
by reaction with carbon dioxide was carried out in a fixed bed
continuous flow double tubular hydrogen transfer reactor using the
same catalyst as that in Example 4. The reaction parameters were
the same as those in Example 4 except the reaction temperature was
600.degree. C. A duplicate experiment was conducted in the closed
conventional reactor to compare and evaluate the hydrogen transfer
reactor. The results are reported in Table E.
TABLE E ______________________________________ Promotion of the
Catalytic Conversion of Natural Gas to Syngas Fuel Intermediate and
Hydrogen by Reaction with Carbon Dioxide in a Hydrogen Transfer
Reactor (Reaction Temperature: 600.degree. C.; All other conditions
including catalyst employed were the same as those in Table D)
Conventional Membrane Reactor Reactor
______________________________________ CH.sub.4 conv. (%) 40.9 48.6
CO.sub.2 conv. (%) 56.6 63.0 H.sub.2 sel. (mol %) 89.8 91.0 CO
yield (mol %) 50.3 54.5 H.sub.2 yield (mol %) 38.1 46.5 H.sub.2 /CO
mole ratio 0.84 0.94 ______________________________________
It is evident from above examples that at 550.degree. C. remarkable
increase in the conversions of CH.sub.4 and CO.sub.2 occurred in
the membrane reactor. Concurrently, yields of CO and H.sub.2 also
increased dramatically (from 21% to 42% for CO and from 16% to 33%
for H.sub.2).
The essential characteristics of the present invention are
described in the foregoing disclosure. One skilled in the art can
understand the invention and make various modifications thereto
without departing from the basic spirit thereof, and without
departing from the scope and range of equivalents of the claims
which follow.
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